Stabilized greases



Patented July 29, 1952 STABILIZED GREASES Eldon L. Armstrong, Garden City, and Richard A. Butcosk, Jackson Heights, N. Y., assignors to Socony-Vacuum Oil Company, Incorporated, a corporation of New York No Drawing. Application September 5, 1951, Serial No. 245,268

3 Claims. 1

The present invention is related to stabilized greases and, more particularly to greases containing ion-exchange resins capable of reducing the increase in acidity of the greases during use. Mineral oils and fatty acid products which are the common components of greases have a tendency to produce acidity; this is particularly true in high-temperature lubrication. When compounding greases it is common practice to so proportion the constituents thereof that the finished grease is slightly alkaline. The consistency and homogeneity of greases depend upon the proper balance of the components and the ultimate acidity or alkalinity of the finished grease. As the free alkalinity in the grease is gradually neutralized by the acids derived from the oxidation of the mineral oil and decomposition of the fatty material, the grease becomes less stable and may finally fall apart, i. e., become granular, thus losing its lubricating power.

It has become common practice to prevent the development of free acidity in greases by providing free alkali in the form of a free base such as sodium hydroxide, potassium hydroxide, hydrated lime and the like, and also by incorporating oxidation inhibitors. However, the amount of free alkali is limited in certain greases because of the decrease of solubility of fatty-acid soaps in mineral oil in the presence of excessive amounts of free base.

It has now been discovered that the detrimental effect of free acid such as develops in greases during use, especially at high temperatures, can be overcome by incorporating ion-exchange resins in greases. Preferably the ion-exchange resins are of the carboxylic acid type and do not adversely afiect the consistency and lubricating properties of the grease when compounded with the conventional components of the grease.

One of the generally accepted industrial tests for the evaluation of lubricating greases from the standpoint of stability to oxidative influences is the Norma-Hoffman test. This test was performed by charging a bomb with a known weight of a sample of the grease under test having a known alkalinity (expressed as per cent sodium hydroxide) or known acidity (expressed as per cent oleic acid) and bringing the pressure in the bomb to 110 pounds per square inch gauge. The bomb, its sample under the aforesaid oxygen pressure, was then maintained at 210 F. for a period of 100 hours or more. During that time the bomb pressure was read at intervals and at the end of the test. The drop in oxygen pressure was taken as a measure of the oxidation stability of the grease being tested. Inasmuch as the products of the reaction between the oxygen and the organic components of the grease are acidic 5 in nature, the test was conveniently supplement ed by a titration of the grease after the test period with a base and the result expressed in per cent oleic acid.

The buffering elfect of the carboxylic acid type ion-exchange agents when incorporated in a lubricating grease and subjected to the Norma- I-Iofiman test is illustrated by the data presented in the following tabulation.

The test greases were made by incorporating one part by weight of the resin under test in 99 parts by weight of a sodium-base grease of conventional composition for example constituted of 23 weight per cent of sodium soap of tallow fatty acids and the balance mineral oil having a viscosity at 100 F. of 300 seconds S. U. V. The resin was worked into the grease until the mixture was visibly homogeneous. The modified grease was then subjected to the Norma-Hofiman test with the results as indicated hereinafter.

Table I Oarboxylic Resin None Acid as Na salt Reaction:

Before Bomb 0.04% NaOHL 0.14% Oleic. After Bomb 2.4% O1eic 1.10% Oleic. Increase in Acidity 2.7% O1eic 0.96% Oleic. Percent Increase inAcidity 100 37.

1 0.04 NaOHoO.28% oleic acid.

A second grease was also prepared and compounded with the free acid form and the alkali metal salt from a carboxylic acid type ion-exchange resin. The grease was made by com: pounding 23% of sodium tallow soap, i. e., sodium salts of the fatty acids of beef tallow typical of the common fatty acids used in grease preparation, with 77% by weight of a lubricating fraction of Mid-Continent oil having a Saybolt Univeral viscosity at 100 F. of 300 seconds. To one portion of the grease about 5 weight per cent of the alkali metal salt form of a carboxylic acid type ion-exchange resin was added and to another portion of the grease about 5 weight per cent of the free acid form of a carboxylic acid type ion-exchange resin was added. The greases were then subjected to the Norma-Hoffman bomb oxidation test with the results tabulated in Table II.

Those skilled in the art will recognize that the original greases to which the ion-exchange resins were added differed. That is to say, one was appreciably more resistant to oxidation than the other. Therefore, while the results cannot be compared directly in a simple quantitative manner, it is manifest that the addition of a carboxylic acid type ion-exchange resin in either the alkali metal salt form or in the free acid form improves the capability of the grease to resist oxidation.

The data presented in the last two columns of Table II establish that both the alkali metal form and the free acid form are effective.

Lime base greases likewise can be stabilized by the incorporation of an ion-exchange resin of the carboxylic acid type. Since the free acid form of the exchange material as well as the alkali metal salt form of the carboxylic acid type of ion-exchange resin is effective it is manifest that the mechanism of stabilization is not the simple one of merely exchanging the alkali metal ion of the exchange material for the hydrogen ion of the free acidsproduced during oxidation.

Thus the present invention provides a means for stabilizing greases by the incorporation therein of about 1 to about 10 per cent by weight of an ion-exchange type resin in the form of particles passing a 100 mesh screen, preferably passing a 200 mesh screen and especially passing a 325 mesh screen. The compositions of the basic greases are not a part of this invention and are well known to those skilled inthe art.

While the foregoing description and discussion has been concerned with soda and lime base greases, it is interesting to note that greases in which the thickening agent is fine silica powder, channel black, polymerized hydrocarbons, etc., likewise are stabilized .by the incorporation of ion-exchange resins. 1 7

As those skilled in the art know, the viscosity of the mineral oil u'se'clft'o prepare satisfactory greases may be varied from about 60 seconds to about 3000 seconds S. U. V. at 100 F. Accordingly', it will be understood that the novel greases can be prepared from mineral oil of lubricating grade having a viscosity between 60 seconds and 3000 seconds S. U. V. at 100 F.

While the ion-exchange resins suitable for stabilizing greases against oxidation, per se, form no part of this invention, it is interesting to note that Kunin and Myers in the text entitled Ion Exchange Resins (pp. 55, 56, 57) have this to say of carboxylic acid type cation exchangers:

Several methods have been suggested for the preparation of exchangers whose cation-exchange activity has been a result of the carboxylic acid group. Fuchs has prepared such materials by. means of oxidizing coal with nitric acid. DAlelio suggests the preparation of such exchangers by the reaction of phenol, acrolein, and the semi-amide of oxamic acid.

Wofatit C, the German carboxylic cationexchange resin has received considerable attention and may be considered as the first carboxylic-type exchanger.

It is prepared from resorcylic acid and formaldehyde in an alkaline reaction mixture.

In U. S. Patent No. 2,340,111, DAlelio describes the preparation of a carboxylic acid ion-exchange material by forming'the'copolymer of a polymerizable mixture comprising at least one polymerizable compound containing a polymerizable CH2 C grouping and at least one other polymerizable grouping, the unsaturated bonds of said polymerizable groupings being non-conjugated with respectto each other, and at least one acrylic acid having the-structural formula:

where R is a substituent selected from the class consisting of hydrogen, chlorine, bromine, monovalent alkyl radicals, monovalent aralkyl radicals, monovalent aryl radicals and monovalent alkaryl radicals.

The present application is a continuation-in part of our copending application Serial No. 111,072, filed August 18, 1949, and now abandoned.

We claim:

1. A grease comprising predominantly a lubrieating fraction of mineral oil, a minor proportion of a thickening agent and an amount of a carboxylic acid type. ion-exchange resin effective to stabilize said grease to oxidation.

2. A grease comprising a lubricating fraction of mineral oil, a metal soap of fatty acids and an amount of a carboxylic acid type ion-exchange resin e'fiective to stabilize said grease to oxidation.

3. A grease comprising a lubricating 'fraction of mineral oil, an alkali metal soap of fatty acids and an amount of a carboxylic acid type ionexchange resin effective to stabilize said grease to oxidation, said resin being present as particles of about325 mesh.

ELDON L. ARMSTRONG. RICHARD A. BUTCOSK.

REFERENCES CITED Thefollowing references are of record the file of this patent:

UNITED STATES PATENTS 

1. A GREASE COMPRISING PREDOMINANTLY A LUBRICATING FRACTION OF MINERAL OIL, A MINOR PROPORTION OF A THICKENING AGENT AND AN AMOUNT OF A CARBOXYLIC ACID TYPE ION-EXCHANGE RESIN EFFECTIVE TO STABILIZE SAID GREASE TO OXIDATION. 